html,body {
    margin: 0px;
    height: 100%;
    overflow: hidden;
}

header,nav,section,article,footer {
    border: 1px solid #ccc;
}

        header {
            height: 13%;
            background-image: url("../img/login_logo.jpg");
            background-repeat: repeat;
            margin: 2px 2px 2px 2px;
        }

        .shang {
            background-color: greenyellow;
            width: 100%;
            height: 6%;
            float: left;
            margin: 2px 2px 2px 2px;
        }

        .o {
            width: 50%;
            margin: 0px auto 0px auto;
        }

        .a {
            width: 100px;
            height: 25px;
            line-height: 25px;
            background: black;
            color: white;
            margin: 5px 10px;
            font-size: 20px;
            font-family: "楷体";
            display: block;
            text-align: center;
            text-decoration: none;
            float: left;
        }

        .a:hover {
            width: 100px;
            height: 26px;
            line-height: 28px;
            color: black;
            background: white;
        }

        .main {
            width: 100%;
            height: 71%;
            float: left;
        }

        .caidan {
            float: left;
            width: 22%;
            height: 100%;
            margin: 2px 1px 2px 0px;
            background-color: rgb(105, 107, 184);
        }

        .zhong {
            float: left;
            width: 54.88%;
            height: 100%;
            margin: 2px 0px 2px 3px;
            background-color: fuchsia;
        }

        .tiao {
            float: right;
            width: 22%;
            height: 100%;
            margin: 2px 2px 2px 1px;
            background-color: crimson;
        }


        .di {
            float: left;
            width: 100%;
            height: 10%;
            background-image: url("../img/555.png");
            background-repeat: repeat;
            height: 45px;
            font-size: 25px;
            color: white;
            margin: 2px 2px 2px 2px;
        }

        #nav {
            width: 150px;
            height: 40px;
            float: left;
            margin: 0 auto;
        }

        ul {
            list-style: none;
        }

        ul li {
            line-height: 40px;
            text-align: center;
            position: relative;
        }

        a {
            text-decoration: none;
            color: #000;
            display: block;
            padding: 0 10px;
            height: 40px;
        }

        a:hover {
            color: #fff;
            background-color: #000;
        }

        ul li ul li {
            float: none;
            background-color: #eee;
            margin-top: 2px;
        }

        ul li ul {
            position: absolute;
            left: 50px;
            top: 20px;
            display: none;
        }

        ul li ul li a {
            width: 80px;
        }

        ul li ul li a:hover {
            background-color: #06f;
        }

        ul li:hover ul {
            display: block;
        }